Processes for the polymerization of olefins in which late transition metal complexes, such as nickel, iron, cobalt and palladium complexes, are used as a polymerization catalyst have improved polymer productivity when an oxidizing agent is present during at least a portion of the polymerization.
Polyolefins, such as polyethylene and polypropylene, are important items of commerce, and many methods have been developed for their production. Commonly a transition metal compound is used as a polymerization catalyst, and recently there has been great interest on the use of late transition metal complexes (Group 8 to Group 10 metals, IUPAC designation) as such polymerization catalysts. While some of these catalysts display excellent productivity of polymer (amount of polymer produced per unit of catalyst) in various types (homogeneous, slurry and gas phase for instance) of polymerization processes, others display relatively low productivity and/or the lifetime of the active catalyst is shorter than that desired in a typical commercial polymerization process.
The cause of these shortcomings for those polymerization catalysts has not been clear, so it has been difficult to rectify them. Generally speaking, while varying polymerization conditions such as temperature, pressure of monomer (if it is a gas), concentration of polymerization catalyst, variation of cocatalyst (such as alkylaluminum compounds), etc., can result in modest improvements in polymer productivity in some instances, often a desired level of productivity is not reached. Therefore methods of making these types of polymerizations more productive are being sought.
U.S. Pat. Nos. 4,710,552, 5,110,928 and 5,210,160 report the use of various halogenated compounds as additives in the polymerization of olefins using Ziegler early transition metal polymerization catalysts, principally to improve the processability of the polyolefins produced. No mention is made of late transition metal catalysts.
WO00/50470 mentions in Example 148 the use of ethyl phenyldichloroacetate in combination with a certain iron containing catalyst in the polymerization of ethylene. There is no mention of any improvement in polymer productivity because of use of the ester.
This invention concerns a process for the polymerization of an olefin, comprising the step of contacting, under polymerization conditions, said olefin with an olefin coordination polymerization catalyst comprising a complex of a Group 8 to Group 10 metal, wherein an oxidizing agent is present during at least a portion of said contacting.
This invention also concerns an improved process for the polymerization of an olefin in which said olefin is contacted, under polymerization conditions, with an olefin co-ordination polymerization catalyst comprising a complex of a Group 8 through a Group 10 metal, wherein the improvement comprises that an oxidizing agent is present during at least a portion of the contacting of said polymerization catalyst and said olefin.
This invention also concerns a process for improving the productivity of an olefin coordination polymerization catalyst comprising a complex of a Group 8 to Group 10 metal, in a process for producing a polyolefin by contacting an olefin with said polymerization catalyst under conditions to polymerize said olefin, said process comprising the step having an oxidizing agent present during at least a portion of the contacting of said olefin and said polymerization catalyst.
In the polymerization processes and catalyst compositions described herein, certain groups may be present.
A xe2x80x9chydrocarbyl groupxe2x80x9d is a univalent group containing only carbon and hydrogen. As examples of hydrocarbyls may be mentioned unsubstituted alkyls, cycloalkyls and aryls. If not otherwise stated, it is preferred that hydrocarbyl groups herein contain 1 to about 30 carbon atoms.
By xe2x80x9csaturatedxe2x80x9d hydrocarbyl is meant a univalent radical that contains only carbon and hydrogen, and contains no carbon-carbon double bonds, triple bonds or aromatic groups.
By xe2x80x9csubstituted hydrocarbylxe2x80x9d herein is meant a hydrocarbyl group that contains one or more (types of) substituents that do not substantially interfere with the operation of the polymerization catalyst system. Suitable substituents in some polymerizations may include some or all of halo, ester, keto (oxo), amino, imino, carboxyl, phosphite, phosphonite, phosphine, phosphinite, thioether, amide, nitrile, and ether. Preferred substituents when present are halo, ester, amino, imino, carboxyl, phosphite, phosphonite, phosphine, phosphinite, thioether, and amide. Which substituents are useful in which polymerizations may in some cases be determined by reference to U.S. Pat. No. 5,880,241 (incorporated by reference herein for all purposes as if fully set forth). If not otherwise stated, it is preferred that substituted hydrocarbyl groups herein contain 1 to about 30 carbon atoms. Included in the meaning of xe2x80x9csubstitutedxe2x80x9d are chains or rings containing one or more heteroatoms, such as nitrogen, oxygen and/or sulfur, and the free valence of the substituted hydrocarbyl may be to the heteroatom. In a substituted hydrocarbyl, all of the hydrogens may be substituted, as in trifluoromethyl.
By xe2x80x9c(substituted) hydrocarbylenexe2x80x9d is meant a group analogous to hydrocarbyl, except the radical is divalent.
xe2x80x9cAlkyl groupxe2x80x9d and xe2x80x9csubstituted alkyl groupxe2x80x9d have their usual meaning (see above for substituted under substituted hydrocarbyl). Unless otherwise stated, alkyl groups and substituted alkyl groups preferably have 1 to about 30 carbon atoms.
By xe2x80x9carylxe2x80x9d is meant a monovalent aromatic group in which the free valence is to the carbon atom of an aromatic ring. An aryl may have one or more aromatic rings which may be fused, connected by single bonds or other groups.
By xe2x80x9csubstituted arylxe2x80x9d is meant a monovalent aromatic group substituted as set forth in the above definition of xe2x80x9csubstituted hydrocarbylxe2x80x9d. Similar to an aryl, a substituted aryl may have one or more aromatic rings which may be fused, connected by single bonds or other groups; however, when the substituted aryl has a heteroaromatic ring, the free valence in the substituted aryl group can be to a heteroatom (such as nitrogen) of the heteroaromatic ring instead of a carbon.
By xe2x80x9cphenylxe2x80x9d is meant the C6H5- radical, and a phenyl moiety or substituted phenyl is a radical in which one or more of the hydrogen atoms is replaced by a substituent group (which may include hydrocarbyl). Preferred substituents for substituted aryl include those listed above for substituted hydrocarbyl, plus hydrocarbyl.
By xe2x80x9c(inert) functional groupxe2x80x9d herein is meant a group other than hydrocarbyl or substituted hydrocarbyl that is inert under the process conditions to which the compound containing the group is subjected. The functional groups also do not substantially interfere with any process described herein that the compound in which they are present may take part in. Examples of functional groups include some halo groups (for example fluoro and some unactivated chloro) ether such as xe2x80x94OR31 wherein R31 is hydrocarbyl or substituted hydrocarbyl. In cases in which the functional group may be near a metal atom, the functional group should not coordinate to the metal atom more strongly than the groups in those compounds are shown as coordinating to the metal atom, that is they should not displace the desired coordinating group.
By an xe2x80x9cactive halocarbonxe2x80x9d is meant a compound that contains carbon and halogen, and optionally hydrogen, and may contain inert functional groups (other than halogen) and, preferably when present in the polymerization process, increases the productivity of the polymerization catalyst by at least 10 percent, based on a similar polymerization without the active halocarbon present.
By a xe2x80x9cneutral bidentate ligandxe2x80x9d is meant a bidentate ligand that no charge on the ligand (is not ionic in a formal sense if not coordinated to the transition metal).
By a xe2x80x9cneutral tridentate ligandxe2x80x9d is meant a tridentate ligand that has no charge on the ligand.
By a xe2x80x9cneutral monodentate ligandxe2x80x9d is meant a monodentate ligand that no charge on the ligand.
By an xe2x80x9cmonoanionic bidentate ligandxe2x80x9d is meant a bidentate ligand that has one negative charge on the ligand (is ionic in a formal sense if not coordinated to the transition metal).
By a xe2x80x9cmonoanionic tridentate ligandxe2x80x9d is meant a tridentate ligand that has one negative charge on the ligand.
By a xe2x80x9cmonoanionic monodentate ligandxe2x80x9d is meant a monodentate ligand that has one negative charge on the ligand.
By xe2x80x9chalogenxe2x80x9d is meant any one or more of fluorine, chlorine, bromine or iodine, and chlorine, bromine and iodine are preferred. Which of chlorine, bromine or iodine is preferred in any particular situation will depend on the particular polymerization process being run, the other ingredients in that process, and which agent is used.
Preferred ligands herein are neutral bidentate ligands, as described in further detail below.
By an xe2x80x9cactivatorxe2x80x9d, xe2x80x9ccocatalystxe2x80x9d or a xe2x80x9ccatalyst activatorxe2x80x9d is meant a compound that reacts with a transition metal compound to form an activated catalyst species. This transition metal compound may be added initially, or may be formed in situ, as by reaction of a transition metal compound with an oxidizing agent. A preferred catalyst activator is an xe2x80x9calkyl aluminum compoundxe2x80x9d, that is, a compound which has at least one alkyl group bound to an aluminum atom. Other groups such as, for example, alkoxide, hydride and halogen, may also be bound to aluminum atoms in the compound. Another useful activator is an alkylzinc compound.
xe2x80x9cNoncoordinating ionsxe2x80x9d (or xe2x80x9cweakly coordinating ionsxe2x80x9d) are sometimes useful in the polymerization processes described herein. Such anions are well known to the artisan, see for instance W. Beck., et al., Chem. Rev., vol. 88, p. 1405-1421 (1988), and S. H. Strauss, Chem. Rev., vol. 93, p. 927-942 (1993), both of which are hereby included by reference. Relative coordinating abilities of such noncoordinating anions are described in these references, Beck at p. 1411, and Strauss at p. 932, Table III. Useful noncoordinating anions include, for example, SbF6xe2x88x92, BAF, PF6xe2x88x92, B(C6F5)4xe2x88x92, or BF4xe2x88x92, wherein BAF is tetrakis[3,5-bis(trifluoromethyl)phenyl]borate.
A neutral Lewis acid or a cationic Lewis or Bronsted acid whose counterion is a weakly coordinating anion may also be present as part of the catalyst system, for example as a cocatalyst (or catalyst activator). By a xe2x80x9cneutral Lewis acidxe2x80x9d is meant a compound that is a Lewis acid capable of abstracting an anion from a late transition metal compound to form a weakly coordination anion. The neutral Lewis acid is originally uncharged (i.e., not ionic). Suitable neutral Lewis acids include SbF5, Ar3B (wherein Ar is aryl), and BF3. By a cationic Lewis acid is meant a cation with a positive charge such as Ag+, H+, and Na+.
In many of those instances in which the transition metal compound does not contain an alkyl or hydride group already bonded to the metal, the neutral Lewis acid or a cationic Lewis or Bronsted acid may also alkylate or add a hydride to the metal, i.e., causes an alkyl group or hydride to become bonded to the metal atom, or a separate compound is added to add the alkyl or hydride group. It is preferred that a neutral Lewis acid which can alkylate or add hydride to the metal, or a combination of a Lewis acid and a compound which can alkylate or add hydride to the metal, be present, and either of these (single or multiple compounds) can be considered an activator. By xe2x80x9chydridexe2x80x9d is meant a single hydrogen atom covalently bound to the transition metal. No particular charge of the transferred hydrogen is implied, i.e., the Lewis acid may formally protonate the metal (transfer H+), but the product is referred to as a hydride.
A preferred neutral Lewis acid which can alkylate the transition metal is a selected alkyl aluminum compound, such as R93Al, R92AlCl, R9AlCl2, (R9AlCl)2O, and xe2x80x9cR9AlOxe2x80x9d (alkylaluminoxanes), wherein R9 is alkyl containing 1 to 25 carbon atoms, preferably 1 to 4 carbon atoms. Suitable alkyl aluminum compounds include methylaluminoxane (which is an oligomer with the general formula [MeAlO]n), (C2H5)2AlCl, C2H5AlCl2, [(CH3)2CHCH2AlCl]2O and [(CH3)2CHCH2]3Al. Preferred alkylaluminum compounds have at least one atom of an element more electronegative than carbon (on Pauling""s electronegativity scale) attached to the aluminum atom. Such elements include halogen, especially chlorine, and oxygen. Another useful alkylating agent is a dialkyl zinc, such as diethyl zinc.
Preferred metals for the transition metal complex herein are Ni, Pd, Fe and Co, Ni and Fe are especially preferred, and Ni is particularly preferred.
Late transition metal complexes useful as polymerization catalysts herein, as well as combinations of two or more late transition metal catalyst, and combinations of late transition metal catalysts with other types of catalysts, are described in U.S. Pat. Nos. 5,714,556, 5,852,145, 5,880,241, 5,929,181, 5,932,670, 5,942,461, 5,955,555, 6,060,569, 6,103,658, 6,174,975, WO96/37522, WO97/23492, WO97/48735, WO98/30612, WO98/37110, WO98/38228, WO98/40420, WO98/42664, WO98/42665, WO98/47934, WO99/49969, WO99/41290, WO99/51550, WO00/50470, JP-A-09255712, JP-A-09255713, JP-A-11158213, JP-A-11180991, JP-A-11209426, EP-A-0893455 and EP-A-0924223, all of which are hereby included by reference for all purposes as if fully set forth. Unless otherwise stated herein, polymerization catalysts for the purposes of the present invention also include catalysts that produce olefin oligomers.
As described in the above-incorporated publications, suitable catalysts are complexes of a late transition metal (Group 8 to Group 10, IUPAC designation) with an organic ligand. Preferred ligands are mono- or bidentate ligands, especially neutral mono- or bidentate ligands. A specific preferred such organic ligand is of the formula (I) 
wherein:
R13 and R16 are each independently hydrocarbyl or substituted hydrocarbyl, provided that the atom bound to the imino nitrogen atom has at least two carbon atoms bound to it; and
R14 and R15 are each independently hydrogen, hydrocarbyl, substituted hydrocarbyl, or R14 and R15 taken together are hydrocarbylene or substituted hydrocarbylene to form a carbocyclic ring.
As examples of when R14 and R15 are each independently a substituted hydrocarbyl may be mentioned when R14 is -YR17R18 and R15 is -ZR19R20, wherein Y and Z are each independently nitrogen, oxygen or sulfur and R17 and R19are each independently hydrocarbyl, or substituted hydrocarbyl or taken together form a ring, and R18 and R20 are each independently hydrogen, hydrocarbyl, or substituted hydrocarbyl, provided that when Y is oxygen or sulfur R18 is not present, and when Z is oxygen or sulfur R20 is not present.
Preferably the late transition metal catalyst is not an iron compound and/or the late transition metal is not coordinated to a tridentate ligand. More preferably this tridentate ligand is not a bisimine of a 2,6-diacylpyridine or a 2,6-pyridinedicarboxaldehyde, and most preferably this tridentate ligand is not 
There are many different ways of preparing active polymerization catalysts of transition metal coordination compounds as described herein, many of which are described in the previously incorporated references (see, for example, U.S. Pat. Nos. 5,714,556, 5,880,241, 6,103,658 and WO00/06620), and those so described are applicable herein. xe2x80x9cPurexe2x80x9d compounds which themselves may be active polymerization catalysts may be used, or the active polymerization catalyst may be prepared in situ by a variety of methods.
For instance, olefins may be polymerized by contacting, at a temperature of about xe2x88x92100xc2x0 C. to about +200xc2x0 C., a first compound W, which is a neutral Lewis acid capable of abstracting an anion to form a weakly coordinating anion; or a cationic Lewis or Bronsted acid whose counterion is a weakly coordinating anion; a second compound such as (II) 
and one or more polymerizable olefins wherein:
M is an appropriate transition metal;
m is the oxidation state of M minus 1;
R13 through R16 are as defined above,
each Q is independently a monoanion, preferably alkyl, hydride, chloride, iodide, or bromide; and
S is a monoanion, preferably alkyl, hydride, chloride, iodide, or bromide.
In this instance it is preferred that W is an alkyl aluminum compound. Other methods for preparing active polymerization catalyst will be found in the previously incorporated references, and in the Examples herein.
The polymerization processes described herein may be run in a xe2x80x9cnormalxe2x80x9d manner as described in the various references listed above for the various late transition metal complexes, with the oxidizing agent present during at least a portion of the polymerization. It is particularly preferred that the oxidizing agent be present (or added) continuously or essentially continuously (for example added periodically, particularly with little time between individual additions) during the polymerization while the components are present, for example, in the appropriate reactor. It is believed that the beneficial effect of the oxidizing agent is enhanced if it is present during most or all of the time the polymerization is taking place. The oxidizing agent not only usually enhances productivity of the catalyst, it also often increases the lifetime of the polymerization catalyst (which of course may also increase productivity depending on how long the polymerization is run).
The polymerization may be run in any of the known ways, for example, it may be a batch, semibatch or continuous polymerization which may be run as a liquid slurry, solution or gas phase polymerization. By xe2x80x9cgas phasexe2x80x9d is meant that the olefin monomer(s) is transported to the reactive polymerization site (i.e., to contact with the catalyst particle) as a gas (except perhaps to diffuse through some polyolefin surrounding the active site), for example in a fluidized bed reactor. Other additives normally present in such polymerizations may also be present herein. For example chain transfer agents such as hydrogen may be present. Such polymerizations are well known in the art, see for instance B. Elvers, et al., Ed., Ullmann""s Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A21, VCH Verlagsgesellschaft mbH, Weinheim, 1992, p. 496-514 and 518-531, which is hereby included by reference.
The polymerization processes herein may be run in the presence of various liquids, particularly aprotic organic liquids. The catalyst system, monomer(s), and polymer may be soluble or insoluble in these liquids, but obviously these liquids should not prevent the polymerization from occurring. Suitable liquids include alkanes, cycloalkanes, selected halogenated hydrocarbons, and aromatic hydrocarbons. Specific useful solvents include hexane, cyclohexane, toluene, benzene, heptane, isooctane, methylene chloride, and 1,2,4-trichlorobenzene.
The olefin polymerizations herein may also initially be carried out in the xe2x80x9csolid statexe2x80x9d by, for instance, supporting the transition metal compound on a substrate such as silica or alumina, or a polymeric material, activating if necessary with one or more cocatalysts, and contacting with the olefin(s). Alternatively, the support may first be contacted (reacted) with one or more cocatalysts (if needed) such as an alkylaluminum compound, and then contacted with an appropriate transition metal compound. The support may also be able to take the place of a Lewis or Bronsted acid, for instance an acidic clay such as montmorillonite, if needed. Another method of making a supported catalyst is to start a polymerization or at least make a transition metal complex of another olefin or oligomer of an olefin such as cyclopentene on a support such as silica or alumina. These xe2x80x9cheterogeneousxe2x80x9d catalysts may be used to catalyze polymerization in the gas phase or the liquid phase.
The process of the present invention can be also used as last step of a multistep process such as described in the WO00/53646, which is incorporated by reference herein for all purposes as if fully set forth. In this process a polymer previously prepared with a different catalyst system is impregnated with the olefin polymerization catalyst system herein and then one or more olefins are polymerized according to the process of the present invention. The polymer of the first steps range from 10 to 70% of the total polymer obtained in the multistep process, preferably from 10 to 60%, more preferably 20 to 50%.
Other details concerning general polymerization conditions may be had by referring to the previously incorporated references.
Although not wishing to be bound by theory, it is believed that the oxidizing agents used herein function by oxidizing lower valent transition metal compounds to higher valent compounds, such as Ni[I] and/or Ni[0] compounds to Ni[II] compounds. It is further believed that the more active form of the polymerization catalyst is a (relatively) higher valent form of the transition metal compound, and that during the polymerization the transition metal is reduced (in an unwanted side reaction) to a lower valent form which is less active or inactive as a polymerization catalyst. The oxidizing agent thus oxidizes the lower valent form of the transition metal to the higher valent, more active form. This regenerates an active polymerization catalyst, thereby increasing the productivity and apparent rate of polymerization of the polymerization catalyst.
An xe2x80x9coxidizing agentxe2x80x9d within the meaning of the present invention, therefore, is an agent capable of oxidizing the transition metal used in the polymerization catalyst, under polymerization conditions, from a lower valent state to the higher valent state to result in a re-activated polymerization catalyst. Thus the oxidizing agent should be a sufficiently strong oxidizing agent (as measured for instance by electrode potentials) to oxidize the appropriate transition metal to the desired oxidation state. The oxidizing agent, however, should not cause significant unwanted side reactions to produce large amounts of byproducts and/or be destroyed before it can carry out the desired oxidation. In addition the oxidizing agent should have some way of contacting the lower valent transition metal atoms, for example be soluble in a liquid medium used in the polymerization, or be volatile enough to be added to a gas phase polymerization process.
The oxidizing agent may be any means suitable for accomplishing the above-stated purpose. Preferred, however, are chemical oxidizing agents such as organic or inorganic compounds with the requisite properties. Preferred of the chemical oxidizing agents are one-electron oxidants. Useful oxidizing agents include, for example, iodine and halocarbons such as perfluoroalkyl iodides, CI4, CHI3, CH2I2, ICH2CH2I, and trityl iodide, preferably iodine. Another preferred oxidizing agent is a benzylic or allylic bromide or chloride such as xcex1,xcex1,xcex1-trichlorotoluene and allyl chloride.
Other useful classes of oxidizing agents and/or individual oxidizing agents include, for example:
NO, NO2, N-bromosuccinimide and O2;
metal cations such as Fe+3, Cu+2, Ag+2, and ferricinium cations;
iminium radical cations such as tris(4-bromophneyl)iminium hexachloroantimonate; and
halogens and pseudohalogens such as BrCN, IBr and ICl.
One type of halocarbon which is useful has the formula 
wherein:
T1 is a hydrocarbyl or substituted hydrocarbyl group containing at least one halogen bonded to a carbon atom; preferably T1 contains 2 or more halogen atoms, more preferably 3 or more halogen atoms;
T2 is hydrogen, hydrocarbyl, substituted hydrocarbyl or a functional group, optionally containing one or more halogen bonded to a carbon atom.
Preferred agents formula (V) are those of the formula (VI):
R19xe2x80x94C(O)xe2x80x94OR20xe2x80x83xe2x80x83(VI)
wherein:
R19 is selected from the group consisting of hydrocarbyl or substituted hydrocarbyl wherein at least one hydrogen atom bonded to a carbon atom is replaced with a halogen atom; and R20 is selected from the group consisting of R19 or hydrocarbyl or substituted hydrocarbyl. Preferably 2 or more, more preferably 3 or more of the hydrogens in R19 are replaced by halogen. R19 is preferably selected from the group consisting of linear or branched, saturated or unsaturated C1-C20 perhaloalkyl, C3-C20 perhalocycloalkyl, C6-C20 perhaloaryl, C7-C20 perhaloalkylaryl and C7-C20 perhaloarylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-16 of the Periodic Table of the Elements wherein xe2x80x9cperhaloxe2x80x9d means that all the hydrogens bonded to the carbon atoms of the correspondent hydrocarbon radical are replaced with halogen atoms. R20 is preferably selected form the group consisting of a C1-C10 alkyl, C6-C20 aryl and C7-C20 alkylaryl.
More preferably the compound of formula (VI) has formula (VII), (VIII) or (IX) 
wherein:
R20 has the meaning given above;
each R23 is independently selected from the group consisting of halogen and R19, preferably each R23 is independently selected from the group consisting of halogen trichloromethyl, perchloroethyl, perchloropropyl, perchlorobutyl; more preferably R23 is halogen;
each R24 is independently selected from the group consisting of hydrogen, halogen and R ; preferably each R is independently halogen, more preferably chlorine;
R25 is selected from the group consisting of phenyl, thienyl, furyl, pyrollyl, pyridyl radicals; preferably R25 is phenyl or a phenyl radical substituted by one or more halogen atoms, preferably chlorine;
X is halogen, preferably chlorine;
Y is selected from the group consisting of hydrogen, halogen, C1-C20 alkyl or C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl, and optionally containing halogen atoms; preferably Y is chlorine;
R26 is selected from the group consisting of linear or branched, saturated or unsaturated C1-C20 perhaloalkyl, C3-C20 perhalocycloalkyl, C6-C20 perhaloaryl, C7-C20 perhaloalkylaryl and C7-C20 perhaloarylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-16 of the Periodic Table of the Elements wherein the suffix xe2x80x9cperhaloxe2x80x9d means that all the hydrogens bonded to the carbon atoms of the correspondent hydrocarbon radical are replaced with halogen atoms, preferably R26 is selected from the group consisting of trichloromethyl, perchloroethyl, perchloropropyl and perchlorobutyl.
Non limitative examples of compounds of formula (VI) are: 
In (V) and any of its preferred forms it is preferred halogen present is chlorine and/or bromine, more preferably chlorine. Especially preferred compounds (VI) are esters of perchlorocrotonic acid or trichloroacetic acid.
Other halocarbons useful in the current process are found in U.S. Pat Nos. 4,710,552, 5,112,928 and 5,210,160, which are incorporated by reference herein for all purposes as if fully set forth. For example, mentioned in these patents are compounds such as allyl chloride, allyl bromide, crotyl chloride, crotyl bromide, propargyl chloride, propargyl bromide, xcex1-chlorotoluene (benzyl chloride), xcex1-bromotoluene, xcex1,xcex1,xcex1-trichlorotoluene, xcex1,xcex1-dichlorotoluene, trichloroacetyl chloride, trichloromethyl vinyl ketone, and other specific compounds that have been previously mentioned herein.
The syntheses of the active halocarbons are well known in the art, and many of them are commercially available.
The chemical oxidizing agent may be introduced into the reactor in any suitable manner. For example in a solution or liquid slurry polymerization it may introduced as a solution in a suitable liquid. Since very little oxidizing agent is required, this additional stream will usually introduce very little xe2x80x9cextraxe2x80x9d liquid into the reactor. In a gas phase reaction the oxidizing agent may be introduced as a vapor, for example as a vapor in ethylene if ethylene is a monomer. This will be particularly useful when elevated temperatures (above room temperature) are present in the polymerization system, since at elevated temperatures the oxidizing agents have higher vapor pressures.
Iodine is preferred and, by iodine herein, it is meant iodine (I2) itself, as well as compounds or combinations of compounds that readily generate iodine, or any chemically equivalent form of iodine such as the triiodide anion (I3xe2x88x92). For example the compound KI3 is soluble in some organic solvent, and may be used in place of I2. Another preferred agent is a benzylic or allylic bromide or chloride such as xcex1,xcex1,xcex1-trichlorotoluene and allyl chloride.
Chemical oxidizing agents are, of course, chemically reactive, and may interact with other ingredients in the polymerization process or even the process equipment. While small amounts of such reactions may not adversely affect the polymerization, substances which may rapidly react with the chemical oxidizing agents may negate their effectiveness. For example it is believed that some activators such as alkylaluminum compounds and dialkylzinc compounds react with iodine to form alkyl iodides and aluminum or zinc iodides. Alkylaluminum compounds that react relatively rapidly with iodine are believed to include trialkylaluminum compounds such as trimethylaluminum and triisobutylaluminum. Aluminoxanes such as methylaluminoxane and dialkylzinc compounds such as diethylzinc react at somewhat slower but still appreciable rates, while alkylaluminum compounds that already contain aluminum halide groups react more slowly. Therefore alkylaluminum compounds such as dialkylaluminum chlorides, alkylaluminum dichlorides, alkylaluminum sesquichlorides and alkylhaloaluminoxanes such as [R1AlCl]2O wherein R1 is alkyl such as methyl, ethyl, propyl and isobutyl are preferred, alkylaluminum compounds, alkylaluminum sesquichlorides and [R1AlCl]2O are more preferred, and alkylaluminum sesquichlorides and [R1AlCl]2O are especially preferred. Even when a compound such as methylaluminoxane or diethylzinc is used, an improvement in productivity is seen, particularly when the concentration of methylaluminoxane or diethylzinc is kept as low as possible, consistent with obtaining a reasonably rapid polymerization rate.
The oxidizing agent is used in an amount (or is present in such a manner) effective to oxidize the transition metal used in the polymerization catalyst, under polymerization conditions, from a lower valent state to the higher valent state. Preferred amounts are sufficient to achieve an at least 10% increase in the productivity of the catalyst (measured in terms of kg polymer/g transition metal).
For chemical oxidizing agents, the molar ratio of oxidizing agent (such as iodine) to transition metal in the reactor feed(s) may vary depending on the particular polymerization system used, for example the activator present, but a generally useful range is a molar ratio of additive to late transition metal of about 5 to about 2000, preferably about 50 to about 1000. The activator may also be continuously or intermittently added to a batch or semibatch reaction. Preferably also the activator to agent ratio should be no less than about 1, more preferably at least about 2.
Any olefin monomer that may usually be (co)polymerized by the late transition metal catalyst may also be polymerized in the process described herein. Copolymers of two or more olefins, and copolymers with other types of polymerizable monomers (for example, carbon monoxide) are also included herein. Which active polymerization catalysts will polymerize which olefins (not all catalysts will polymerize all olefins or combinations of olefins) will also be found in the above listed references. Monomers useful herein include ethylene, propylene, other xcex1-olefins of the formula R2CHxe2x95x90CH2, wherein R2 is n-alkyl containing 2 to about 20 carbon atoms, cyclopentene, a styrene, a norbornene, and an olefin of the formula H2CHxe2x95x90CHR3Z, wherein R3 is alkylene or a covalent bond, preferably xe2x80x94(CH2)nxe2x80x94 wherein n is an integer of 1 to 20 or a covalent bond, more preferably a covalent bond, and Z is a functional group, preferably xe2x80x94CO2X, wherein X is hydrogen, hydrocarbyl, especially alkyl, or substituted hydrocarbyl. Preferred monomers are ethylene, propylene and cyclopentene, and ethylene is especially preferred. Also preferred are copolymers in which ethylene is a monomer.
As indicated above, the oxidizing agents may chemically interact with the process equipment, so appropriate materials of construction should be used for the reactors used in the polymerization process herein. Thus the addition of any particular oxidizing agent may require the use of materials of construction that are resistant not only to the oxidizing agent but any products of reaction of that compound.
In the Examples the following abbreviations are used:
n-BPCCxe2x80x94n-butyl perchlorocrotonate
ETAxe2x80x94ethyl trichloroacetate
DSCxe2x80x94differential scanning calorimetry
GPCxe2x80x94gel permeation chromatography
IBACOxe2x80x94isobutylchloroaluminoxane
I.V.xe2x80x94intrinsic viscosity
MMAOxe2x80x94modified (with butyl groups) methylaluminoxane
Mnxe2x80x94number average molecular weight
Mwxe2x80x94weight average molecular weight
PExe2x80x94polyethylene
RTxe2x80x94room temperature
Tmxe2x80x94melting point
In the Examples, all pressures gauge pressures. Except where otherwise noted, the nickel compound used was (III) 
Another nickel compound used was 